KT77 bias.

Nixxuz

Super Member
I apologize if I've asked this before. I got a quad of Gold Lion KT77's and while the sound is great, it's also realllllly analytical. Like I'm hearing an assembly of musicians, all in the same room, but it's not that kind of amorphis "song" that I'm used to hearing. It's not exactly "off-putting", but it's distracting in a way I've not felt before. So is this a good thing or a bad thing? I mean, I used to just enjoy big loud speakers that were super dynamic. Then I stepped into some more neutral speakers and started getting into the nuance of the music. So maybe this is another step in another direction? I hesitate to use the term "better" or what have you.

Anyway, I'm wondering if this might be because I'm running these KT77's towards the bottom of the suggested bias for my amp. Manual states 3.5 to 4.0mv. I've read that 77's bias high. Should I be pushing them toward that higher end? Because I've also heard that running the lowest bias you can get away with preserves tube life.

Any thoughts or suggestions?
 
The only successful try of the GL KT77 I had is with the Marantz 8b. Everywhere else I tried them was exactly as you described. Clear but very thin sound.

Also they don't bias like a EL34 so depending of the amp, it's not a swap: sometimes you need to adjust the bias range in order to get them right. But then it's not necessary good for a "normal" el34 so... I had exactly this situation with the Fairchild 255A. So I decided to go back to EL34 native.

I don't know what amp you have so without the operating plate voltage of the tubes, it's pretty hard to say.
Let's say your amp has a B+ of 500V, very classic, 4mV I assume equal to 40mA, put you perfect class A range below 80%.

So go for 4 mV then, as running them harder will help the sound, and reduce distorsion, especially on a UL topology.
You can always dial it down if you don't see improvement you you feel the tubes getting too hot for your taste.

If you want a full bodied sound, try the EH 6CA7EH (EH version, not the regular one) instead. These are not pricey and really rock, worth a shot really.

I run them in an UL120 amp designed for KT77 and they really outperform the GL KT77 I've tried on this amp.

My 2 cents :)
 
The only successful try of the GL KT77 I had is with the Marantz 8b. Everywhere else I tried them was exactly as you described. Clear but very thin sound.

Also they don't bias like a EL34 so depending of the amp, it's not a swap: sometimes you need to adjust the bias range in order to get them right. But then it's not necessary good for a "normal" el34 so... I had exactly this situation with the Fairchild 255A. So I decided to go back to EL34 native.

I don't know what amp you have so without the operating plate voltage of the tubes, it's pretty hard to say.
Let's say your amp has a B+ of 500V, very classic, 4mV I assume equal to 40mA, put you perfect class A range below 80%.

So go for 4 mV then, as running them harder will help the sound, and reduce distorsion, especially on a UL topology.
You can always dial it down if you don't see improvement you you feel the tubes getting too hot for your taste.

If you want a full bodied sound, try the EH 6CA7EH (EH version, not the regular one) instead. These are not pricey and really rock, worth a shot really.

I run them in an UL120 amp designed for KT77 and they really outperform the GL KT77 I've tried on this amp.

My 2 cents :)
Amp is a Yaqin MC13S. I've found by dialing up my sub a bit and upping the crossover it's come a bit more into it's own. But thanks for the advice! Still playing with tubes all the time.
 
I use KT-77's in my VTA ST-70. I have them biased at 40. They have been running like that for some time now without any problems.
 
I can't comment on KT77's bias, my amp is autobiasing, but I would describe the sound very differently. Vivid, colorful, and organic with great detail is how I describe the Gold Lions in my amp, a one off Deja Vu stereo triode class A amp.
 
The only successful try of the GL KT77 I had is with the Marantz 8b. Everywhere else I tried them was exactly as you described. Clear but very thin sound.

Also they don't bias like a EL34 so depending of the amp, it's not a swap: sometimes you need to adjust the bias range in order to get them right. But then it's not necessary good for a "normal" el34 so... I had exactly this situation with the Fairchild 255A. So I decided to go back to EL34 native.

I don't know what amp you have so without the operating plate voltage of the tubes, it's pretty hard to say.
Let's say your amp has a B+ of 500V, very classic, 4mV I assume equal to 40mA, put you perfect class A range below 80%.

So go for 4 mV then, as running them harder will help the sound, and reduce distorsion, especially on a UL topology.
You can always dial it down if you don't see improvement you you feel the tubes getting too hot for your taste.

If you want a full bodied sound, try the EH 6CA7EH (EH version, not the regular one) instead. These are not pricey and really rock, worth a shot really.

I run them in an UL120 amp designed for KT77 and they really outperform the GL KT77 I've tried on this amp.

My 2 cents :)
Well, I tried for another day and rolled the stock 6CA7's back in. All the magic came back! Put em' on BT and they were sold in less than an hour. Hopefully they do for the buyer what I couldn't get from them. Like you said. it was very detailed, but somehow "thin". I'm thinking about trying a set of EL34's to see what that sounds like.
 
Interesting.

Is your 6CA7 the EH version from Electro-Harmonix? It's a EL34 on steroid. Bigger bottle but they are really good.

The TungSol EL34B is supposed to be very good. I just bought a quad and will try them in my Fairchilds.
 
Mine are branded Yaqin. They actually look pretty neat, but I have heard they are "ok". Now that's always the view of people who are reviewing OTHER tubes they just bought. Which will, of course, sound "better". I may try some of the EH "fat bottles". I've also heard good things about the Tung Sol's. Might even try the Mullards.
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Funny how much we're willing to spend on a small improvement and hear/say......It's the same with film caps....
You can't reallly blame people for wanting to try different tubes, afterall, back in the day the tube manufacturers would all hype their own brand over the others for different reasons. Besides, if they did not want you to play with different tube types, why would they make the tubes so easy to change out?
 
"Back in the day" an EL34 was an EL34; a 6L6GC was a 6L6GC. Nobody considered that one brand would sound different than another. Sometimes "back in the day" there was no choice: you bought whatever brand the store sold. In the 1970s and 1980s there was very little choice at the local electronics store; all they sold at my local store was "Standard Brand." I remember trying to find 7581s for my Citation V about 1978. What I received in my "Standard Brand" box labeled "7581" was Russian 6P3C. I don't think they lasted more than a week.
 
I have a Silk (=Yaqin) MC-30L that came with the Shuguang Blue-bottle 6CA7 tubes mentioned above. After three years, I decided to try something new and got a matched quad of JJ KT 77 tubes. As they have a reputation for being robust, I'm biasing them at .45 volts, up from the .4 volt recommendation for the 6CA7's. My initial impression is that the KT 77's are more balanced. But as with so many things in audio, are they better? I don't really know but they sound nice and were not a large investment. Whereas many folks are not fans of JJ tubes, I've used some EL84's in my Magnavox 9300-series amp and some JJ 12AU7's in my Grounded grid preamp and they have all performed well.
 
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